MFJ-269D Instruction Manual LF/HF/VHF/UHF SWR Analyzer
18
5.4.1.4
Return Loss and Reflection Coefficient
To access
Return Loss and Reflection Coefficient
, enter Advanced-1 and press the
Mode
button once.
You may also access it from any other mode in Advance-1 by stepping through the menu using the
Mode
button. The entry screen is shown below:
The
Return Loss and Reflection Coeff
mode measures and displays
Return Loss
in dB along with the
Voltage Reflection Coefficient
. These measurements are alternative terms that describe SWR. In this
mode, the analog meters indicate SWR (normalized to 50 Ohms) and Impedance (Z). To use this mode,
connect the DUT to
Antenna
and adjust the VFO for
Frequency
. Sample display screens are shown
below:
5.4.1.5
Resonance
To access
Resonance Mode,
enter Advanced-1 and then press
Mode
twice. If already in Advanced-1,
scroll to it using the
Mode
switch. The entry screen is shown below:
Resonance Mode
draws attention to reactance, displaying it on the
Impedance
meter as an analog tuning
aid for identifying resonance. In this mode, the MFJ-269D measures and displays
Frequency
,
SWR
,
Resistance (
Rs
), and Reactance (
Xs
). When reactance equals
zero
in a system that has selectivity, the
system
is said to be
resonant
.
Note:
Because of transmission line effects, zero-reactance (or resonance) can occur on frequencies
where the antenna is
not
actually resonant. Conversely, an antenna may
appear
to contain reactance even
at its true resonant frequency when it is measured through a feedline. A less-than-perfectly matched
antenna and feedline, when used with a feedline that is not an exact multiple of 1/4 wavelength (0, 1/4,
1/2, 3/4, etc.), will have reactance added by the feedline. Reactance added by a non-quarter wave
multiple mismatched feedline may coincidentally cancel a non-resonant antenna’s reactance, making the
system resonant.
The SWR of the system, if the feedline is a true 50-ohm feedline (or any impedance feedline that matches
the normalized (Zo) impedance setting of the instrument) with minimal loss and free from common mode
currents, will not change as the feedline length is changed. This is true even if the resonant frequency or
reactance changes.